Heretofore known devices for applying glue to fibers, according to which a shaft centrally arranged in a drum-shaped mixing chamber, has tools rotating thereon in the operating range of which the mixed substance passes after glue has been added, are employed for applying glue to fibers as well as to chips or the like. The design of these heretofore known machines is based on the finding that for purposes of obtaining a homogeneous mixture a particularly well distributed addition of the glue is of less importance than a fast homogenization of the mixed substance after the addition of glue by moving the chips or the like under a moderate pressure relative to each other. Such chip movement will cause the glue which is supplied to the chip material to become distributed uniformly in the material.
For purposes of obtaining the wiping effect between particles or fibers of the material which will result in uniform distribution of the glue thereon, the tools in the mixing zone adjacent the glue applying zone are in most instances provided with front surface portions of substantial area which are inclined toward the advancing direction and which, while the mixing substance is being agitated, exert a moderate pressure on the material and thus press the particles against each other.
Due to the simultaneously generated relative movements between the particles, an intensivewiping of the glue therebetween will be realized. During the agitation of the material being mixed, those particles which are adjacent the tool slide along the inclined surface parts of the tool while due to the lateral deviation of the adjacent particles relative to the advancing direction of the tools, the pressure required for an intensive wiping effect is generated in the adjacent mixed substance. Under the influence of this pressure, the adjacent material starts moving and escapes toward the side while, however, the pressure in the material by a correspondingly long design of the inclined sliding surfaces on the tool can be maintained also during this escaping movement.
Therefore, an intensive wiping of the glue by friction within the material requires distinct sliding operations of the material along the tool so that such tools in their range of operation may heat up and may have to be cooled by special cooling operations.
While with apparatus of the nature described, a uniform application of glue to chips and particles and the like can be obtained in such a manner so that it becomes possible to produce veneer or plywood plates of high qualities, experience has shown that fiber plates produced from fibers to which the glue has been applied in this manner have properties which reduce the quality.
More specifically, such fiber plates contain a plurality of brittle glue enclosures in the form of nests or spots. The felting of the individual fibers in the plates as it is desired in order to obtain high strength, is harmfully effected by ball-shaped rolled up agglomerates which are created by tools on the shaft having broad surface areas which engage the mixture of glue and fibers. Furthermore, such plate contains enclosures of quantities of fiber particles which have received too much glue and are compressed to a too-great extent and, in addition thereto, have the fibers oriented in one direction, said quantities of fiber particles having been formed by the formation of deposits on machine parts of the glue applying device.
Such faults in the fiber plate are all the more serious since such fiber plates, due to their homogeneous felted and layer-free texture, may be qualitatively particularly high-grade plates and may be particularly solid and well machinable. The above-mentioned faults, when occurring in the finished fiber plate, reduce, however, the important fundamental advantages of a fiber plate so that such fiber plates heretofore could frequently not be used because it was not possible to manufacture the same substantially free from faults and in an economical manner.
Experience has shown that glue-fiber agglomerates are formed by the friction and wiping effect which is favorable for the application of glue to the chips, and it was, furthermore, found that heretofore known machines and tools due to their flat design offer too much sliding and rolling-up surfaces to the fiber-glue mass. Due to the distinctive sliding movement between the mixed substance and the sliding surfaces of the tool which sliding movement and sliding surfaces are necessary for obtaining a good intermixture of the glue during the application of the glue to the chips, the fibers containing a high proportion of glue are held in this position.
This brings about the formation of ball-shaped rolled-up glue-fiber agglomerates with frequently too high a proportion of glue. On the other hand, a wiping of the glue within the adjacent regions of the material occurs only to a rather limited extent so that the glue enclosures are not broken up.
The problem underlying the present invention consists in so designing the glue application of the above-mentioned general type that a rolling-up or a formation of nests in the fiber material after the addition of glue will be avoided.